森 治

Copyright © 2020 by the International Astronautical Federation (IAF). All rights reserved. The removal of space debris from an orbit is one of the definitive solutions to the increasing Earth-orbiting satellites issue. To achieve active removal of space debris, accurate estimation of the state of motion of the target is crucial. In addition to that, a safe approach is preferable. Many strategies have been proposed for estimation of motion of a non-cooperative target, but there are still problems with regards to conducting precise, robust and cost-effective estimation in real-time. This study proposes a new strategy to solve this issue - a real-time and practical method based on optical navigation around small bodies. A computer simulation results show the efficacy of the proposed method and verifies that it can be a viable option for use in the capture of non-cooperative space debris targets.

© 2020 by the International Astronautical Federation (IAF). All rights reserved. Two novel approaches to maximise structural flatness and minimise perturbation solar radiation torque on 100 m class interplanetary solar sails are presented. First, allowing the length of central tethers to be actuated to maximise sail flatness in orbit. Second, replacing the central tether with rigid booms with controllable length and extension angle, to move the centre of solar radiation pressure with respect to the centre of mass. The performance of the above two methods are analysed by using analytical and numerical techniques. While the large sail size requires a high degree of sail flatness (<1 degree), the results show that the two methods can satisfy this requirement, paving the way towards 100 m class deployable space structures, and an entirely new class of space missions.

© 2020 by the International Astronautical Federation (IAF). All rights reserved. JAXA and other organizations are considering transformable spacecraft. The transformable spacecraft is a spacecraft that can change its structure. Utilizing these characteristics, this spacecraft has an engineering challenge to perform attitude control without fuel using the non-holonomic properties and the solar radiation pressure. The mission that is being considered is an on-orbit interferometer, which requires highly accurate attitude stability. In transformable spacecraft, the effects of solar radiation pressure can be controlled by structural changes. This allows the solar radiation pressure to be used for attitude control. In addition, an equilibrium point can be created by structural changes. The equilibrium point is an advantage in stabilizing the posture because the torque caused by solar radiation pressure due to the posture change is reduced. It is considered that attitude control around the stable equilibrium point is relatively easy. If a control method around the unstable equilibrium point can be established, the mission range will be greatly expanded. In this study, we propose a method for attitude stabilizing control of transformable spacecraft at unstable equilibrium point using solar radiation pressure. The proposed method identifies the equilibrium point as well as stabilizes the attitude. Numerical analysis confirmed the effectiveness of the proposed method under certain constraints. However, the proposed method has a large manual aspect and is limited only to certain constraints. Therefore, in this study, in addition to the proposed method, we will consider stabilizing the attitude of the spacecraft by reinforcement learning.

© 2020 by the International Astronautical Federation (IAF). All rights reserved. A solar sail is not only propelled by solar radiation pressure (SRP), but also generates torque using SRP. When a sail membrane's shape is not flat, unexpected torque due to SRP is generated. It is necessary to control the sail membrane's shape and the resulting SRP torque to operate a solar sail for long periods and to reduce fuel consumption. Membrane shape control is a common issue not only in solar sails but also in space membrane structures. Therefore, we propose a method to actively control the in-plane and out-of-plane torque by deformation of the membrane shape using Shape Memory Alloy wires (SMA wires). An SMA wire is a type of a soft actuator that contracts when heated. In the proposed method, the SMA wires are attached at several locations on the sail membrane, allowing the entire membrane to deform in out-of-plane at the locations where the SMA wires contract. Furthermore, it is possible to control the membrane shape depending on the situation by selectively contracting subsets of SMA wires. In this paper, a finite element analysis and an experiment were conducted under the same condition to validate the numerical modeling for the SMA wire actuation. As a result, the validity of the membrane shape analysis could be shown since the tendency of the membrane shape deformation was the same in the experiment and the analysis. Next, the relationship between the SMA wire positions and the resulting SRP torque is clarified via another numerical analysis. Results show that in-plane and out-of-plane torques can be produced, respectively by contracting the SMA wires in line-symmetric and point-symmetric manners.

Copyright © 2020 by the International Astronautical Federation (IAF). All rights reserved. During the touchdowns of the "Hayabusa2" spacecraft on the asteroid Ryugu, some of the ejected surface materials were scattered toward the spacecraft. Apart from impact sampling by firing a metallic projectile, another mechanism of this phenomenon is surface material ejecta from formation of a crater by RCS thrusts of the spacecraft during its ascent from the asteroid surface after the touchdown. We conducted ground experiments of gas injection into simulated soil under vacuum in order to investigate the interaction between thruster plume and asteroidal regolith.

Copyright © 2020 by the International Astronautical Federation (IAF). All rights reserved. Transformable spacecraft under development is an innovative system that consists of several structural components, such as panels, connected together by internal force actuators. The spacecraft can change its structure drastically by driving installed actuators and achieve the following four features simultaneously. The first feature is "attitude change by internal force using non-holonomic characteristic of the system". It is possible to orient the spacecraft to an arbitrary direction by repeating the deployment of the panel in an appropriate order by the internal force actuator. The second feature is that "change of the structure enables the multiple functions by switching modes". Two telescopes will be installed for scientific missions utilizing the features of the transformable spacecraft and used to realize two different observation modes. One is a mode in which each telescope is oriented to different directions to perform wide-field observation (single telescope mode). The other is a mode in which two telescopes are pointed in the same direction. This mode enables the spacecraft to work as an interferometer (interferometer mode). The third feature is "orbit control and orbit keeping by controlling the solar radiation pressure on the spacecraft with the use of change of spacecraft structure". Since the spacecraft can change its structure by the internal force actuator, the orbit control and orbit keeping are achieved without fuel consumption. By utilizing this feature, the spacecraft will be injected into an artificial halo orbit around Sun-Earth Lagrangian point L2, and the technology demonstration of the transformable spacecraft and the observation mission will be performed in the orbit. The fourth feature is "passive cooling of observation equipment by use of panels as sunlight shield". In the observation mode, observation in the infrared region is performed and sufficient cooling is required. Appropriate arrangement of panels enables shielding of sunlight, and then the passive cooling of the observation equipment is realized. As a result, disturbance due to refrigerator is eliminated, which contributes to precise observation in addition to the contribution by non-holonomic attitude control without disturbance. This paper shows the analysis and experimental results for feasibility studies and conceptual designs of above four features. Furthermore, development status of the system and each subsystem to realize the spacecraft are introduced.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. The membrane dynamics of spinning solar sails have a special relevance when considering attitude control of the spacecraft. So as to model the system accurately, the bending stiffness of the membrane has been included in the numerical approach, as it is believed to have strong effects on the behavior of the sail. First, this study shows that the influence of the bending moment on the attitude of the sail during its spin axis reorientation should not be neglected. Given the difficulty of measuring the actual bending stiffness of the membrane, finding a control system capable to perform the same regardless of its value is necessary. Therefore, this paper presents a new control system and its corresponding logic to lower the influence of the bending parameter on this attitude maneuver performance. Finally, a frequency analysis on the vibrations arising in the membrane when considering different bending stiffness values is done. This last analysis shows the shift in the natural frequencies obtained, remarking the importance of the bending stiffness when considering the dynamics of a mast-free sail.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. In this study, we modify multi-particle method, a calculation method for predicting membrane behaviour, for evaluating collision between membranes and the change in membrane compression and bending stiffness due to devices mounted on membrane. This modification is verified its validity by the consistency with the results of the experiments conducted in the previous study. Then, we investigate the changes in the deployment behaviour when the temperature and thickness of solar cells change.